The Nuclear and Industrial Safety Agency will revise regulations on coolant water pipes at nuclear plants and write a guideline in the wake of Japan’s deadliest atomic plant accident, agency officials said Wednesday.
Currently, there is no guideline or standard on how, which parts and how frequently the pipes for the so-called secondary coolant water must be checked. Nuclear plant operators are only required to report to the government the results of annual inspections.
In Monday’s accident at the Mihama Nuclear Power Plant in Fukui Prefecture, four workers were killed and seven were injured by superheated steam escaping from a ruptured pipe. The plant’s operator, Kansai Electric Power Co., failed to inspect the pipe during the 27 years since the reactor began service in December 1976.
The safety agency, part of the Ministry of Economy, Trade and Industry, said it will set up a panel of experts to discuss whether the government’s oversight was appropriate and what kind of rules are needed to ensure proper management of the pipes.
But it has yet to decide whether the common guideline is to be compiled as legislation or as an industrial standard, the agency said.
By design, pressurized water in the secondary loop that goes through the steam generator to activate the turbine is not radioactive because it does not mix with water from the primary system that runs through the reactor.
As a result, water pipes on the secondary loop currently fall under the same regulations as pipes in thermal power plants, according to the agency.
With no common guideline set by the government, each power company carries out inspections under its own rules and the government only receives reports on annual inspections.
Kepco was, therefore, not legally required to inspect the corroded pipe in Monday’s accident.
Having failed to fully assess the state of similar nuclear reactors in the country so far, the government is now gathering information on the 23 other pressurized-water reactors. Most of the pipes at these reactors have already been, or are scheduled to be, replaced.
It was found after Monday’s accident that the carbon steel pipe that burst had been corroded by the pressurized coolant water to a thickness of only 1.4 mm, compared to the original 10 mm.
Kepco admitted Tuesday that despite being notified in November of the need for inspections by a subcontractor that services the plant, it had still not checked the pipe.
Sources said Wednesday that a Kepco employee at the Mihama plant allegedly followed a manual blindly even after seeing signs of trouble and delayed notifying the fire department by more than 10 minutes.
The fire alarm of the plant’s No. 3 reactor went off at 3:22 p.m. Monday, but Kepco alerted the fire department 13 minute later at 3:35 p.m., according to Kepco and other sources.
Kepco allegedly failed to notify the fire department after the alarm signaling abnormalities went off and the turbine automatically shut down, the sources said.
According to the Kepco manual, when a fire alarm is activated, employees are supposed to identify the location and magnitude of the fire before contacting the appropriate agencies.
Although the turbine facility was filled with steam, the employee followed the manual instead of calling the fire department, because he thought it was a false alarm, the sources said.
Meanwhile, Mizuho Fukushima, the leader of the Social Democratic Party, visited Mihama on Wednesday to meet with Kepco President Yosaku Fuji and demand an end to nuclear power development.
Monju decision on hold
FUKUI (Kyodo) Fukui Gov. Issei Nishikawa suggested Wednesday the prefectural government might significantly delay its decision on whether to retool the trouble-plagued Monju fast-breeder reactor.
Asked how long the it would take to reach a decision, Nishikawa replied, “We won’t know it until problems (concerning Monday’s accident) are resolved.” On Monday, there was a fatal accident at Mihama Nuclear Power Plant in the prefecture.
The governor also suggested that his government would request a suspension of the pluthermal nuclear power project at Takahama Nuclear Power Plant.
Both the Mihama and Takahama plants are owned by Kansai Electric Power Co., based in Osaka.
Fukui Prefecture has 15 nuclear power reactors, the largest number of the nation’s 47 prefectures.
Pluthermal, or plutonium-thermal power generation, is designed to use mixed uranium-plutonium oxide fuel, which allows natural resource-scarce Japan to make use of spent fuel at nuclear reactors for power generation as well as to unload a growing volume of spent nuclear fuel.
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